This invention concerns amber polyester compositions, which are suitable for packaging food and beverages wherein blockages of ultraviolet and visible light is important. More specifically, this invention is concerned with providing an amber polyester composition that significantly absorbs light of wavelengths shorter than about 550 nm, which is achieved by a novel combination of several colorants, most of which are copolymerized into the polyester.
The packaging of beverages and food in plastic containers places a particularly challenging set of technical specifications on the polymer from which a container is produced. The container must prevent an excessive loss of carbonation through the walls of the container and must limit the ingress of oxygen to a very low level. Also, with some foods and beverages it is very desirable to protect them from ultraviolet light and some wavelengths of visible light.
Particularly problematic is providing suitable polyester packaging for beer. Although a few beers are specifically treated to be resistant to light-induced changes, most beers are highly sensitive to light. As a result, the container or package must block the damaging portions of the light spectrum. The light-induced changes that occur to produce the characteristic light-struck or xe2x80x9cskunkyxe2x80x9d flavor are well documented, for example by J. Templar, K. Arrigan, and W. J. Simpson, Brewer""s Digest, Vol. 70, no. 5, pages 18-25 (1995) and references therein. It is generally accepted that not only ultraviolet light but also visible light of wavelengths shorter than about 550 nm are responsible for the formation of the light-struck flavor (Vita Biundo, Master Brewers Association of the Americas Technical Quarterly, Vol 37, no. 2, pp. 233-238. and J. Templar, K. Arrigan, and W. J. Simpson, Brewer""s Digest, Vol 70, No. 5, pp 18-25 (1995).). It is therefore desirable to produce a polymer for packaging beer that blocks a large portion of ultraviolet and visible light with wavelengths of less than 550 nm from reaching the beer.
Polyesters having colorants and other light-absorbing compounds copolymerized therein are well-known. U.S. Pat. No. 4,617,373 discloses the use of certain copolymerizable methine dyes at concentration from 1 to 5,000 ppm in condensation polymers including an amber poly(ethylene terephthalate) formulation. However, the light protection provided by this formulation falls far short of the light protection requirements of most beers. U.S. Pat. No. 4,617,374 discloses polyester compositions comprising poly(ethylene terephthalate having copolymerized therein certain methine UV-absorbing compounds, but does not mention the use of the methine UV-absorbing compounds to produce a light protecting amber colored polyester.
U.S. Pat. No. 4,745,173 discloses the use of 1 to 20,000 ppm of colorants having the 2,5-diarylaminoterephthalate chromophore. The ""173 patent mentions the use of such colorants in the production of amber colored polyester but does not mention any specific formulations that meet the light protection requirements of most beers. U.S. Pat. No. 4,390,570 discloses the use of certain anthraquinone dyes as colorants in polyesters for food and beverage packaging. Again, the possible use of such dyes in an amber formulation is mentioned, but no specific combination of colorants for the production of an amber polyester suitable for packaging beer is given.
The present invention provides an amber polyester composition that significantly absorbs light of wavelengths shorter than about 550 nm and is particular suitable for the production of containers or packaging material intended for the packaging of beer. Accordingly, the present invention provides a molding grade amber composition comprising a thermoplastic polyester having copolymerized therein or reacted therewith residues of at least two compounds of formula I at least one compound of formula II and at least one compound of formula III: 
wherein:
R is selected from hydrogen, fluorine, chlorine, bromine, trifluoromethyl, C1-C6-alkyl and C1-C6-alkoxy;
R1 and R2 are independently selected from C1-C8-alkyl; C1-C8-alkyl substituted with one or two groups selected from hydroxy, cyano, C1-C6-alkoxy, (OCH2CH2)1-3xe2x80x94O C1-C6-alkoxy, carboxy, halogen, C5-C7-cycloalkyl, C2-C6-alkoxycarbonyl, C2-C6-alkanoyloxy, aroyloxy, C2-C6-alkoxycarbonyloxy, heteroarylthio, aryloxy, arylthio, N-arylcarbamyloxy and aryl; C3-C8-alkenyl; C5-C7-cycloalkyl; aryl; R1 and R2 in combination may be a single group such as pentamethylene, ethyleneoxyethylene or ethylenesulfonylethylene; R1 and (R)n in combination may be a trimethylene group optionally substituted with one or two C1-C8-alkyl groups which with the benzene ring to which R is attached forms a 1,2,3,4-tetrahydroquinoline radical; or R1 may represent the radical: 
wherein P and Q are defined below;
P and Q are independently selected from cyano, aryl, C2-C6-alkoxycarbonyl, C1-C6-alkylsulfonyl, arylsulfonyl, carbamyl, Nxe2x80x94C1-C6-alkylcarbamyl, N-arylcarbamyl and heteroaryl;
R3 is selected from hydrogen, C1-C6-alkyl, C1-C6-alkoxy, aryl, cyclohexyl, aryloxy, arylthio, C2-C6-alkoxycarbonyl, trifluoromethyl, hydroxy, C2-C6-alkanoylamino, aroylamino and halogen;
Y is selected from hydrogen, C1-C6-alkyl, aryl, C5-C7-cycloalkyl, xe2x80x94CH2xe2x80x941,4-cyclohexylenexe2x80x94CH2OH, (CH2CH2O)1-2 CH2CH2OH; C3-C7-alkenyl, and furfuryl;
R4 is selected from hydrogen, C1-C6-alkyl, C1-C6-alkoxy or halogen;
R5 is selected from hydrogen or one of the groups which Y may represent;
m is 1, 2, or 3; and n is 1 or 2;
provided that at least one polyester reactive group be present on the compound of formulas I, II and III; and wherein the concentration of the copolymerized compounds is sufficient that a film of the polyester composition having a thickness of from about 25 to 1016 microns (about 1 to 40 mil) transmits no more than an average of about 3% of ultraviolet and visible light over the wavelength range from about 300 to 450 nm, no more visible light than an average of about 7% over the 450 to 500 nm wavelength range and no more visible light than an average of about 15% over the range of from about 500 to 550 nm; and wherein about 50-200 ppm of copper phthalocyanine (C.I. Pigment Blue 15) blue colorant is admixed in the thermoplastic polyester. The reference herein to copper phthalocyanine includes C.I. Pigment Blue 15, 15:1, 15:2 and 15:3 crystalline forms.
The amber colored polyesters of the invention are useful for forming bottles or other containers for packaging food and beverages, particularly beer. The coloration of the polyester is such that a substantial portion of ultraviolet and visible wavelengths shorter than about 550 nm are prevented from reaching the contents of the container. Through the process of copolymerization, the colorants having formulas I, II and III are rendered highly resistant to extraction by foods and beverages. The polyester is not limited to use in containers that consist of only a single layer of such a polyester, but can also be used in one or more layers of a multi-layer container. If desired, the polyester can be admixed with other materials. Such other materials may be recycled polyester or substances that impart gas barrier or oxygen scavenging properties.